Well pumping units have traditionally included a drive mechanism having an output of rotary motion, such as a rotating shaft, a vertically-reciprocating polish rod assembly, and working parts which translate the rotary motion into vertical motion to operate the polish rod assembly.
It is known to use an endless chain and sprocket assembly to translate the rotary motion from the drive mechanism to vertical motion to operate the polish rod assembly. Such endless chain and sprocket assemblies usually include at least two sprockets spaced vertically with the chain in engagement with the sprockets. One of the sprockets is attached to the rotating output shaft of the drive mechanism. A member is usually attached to the endless chain and thus orbits with the chain around the sprockets.
This member may be a sliding arm which slides horizontally in guides, the guides being restricted to vertical movement only. The guides usually slidably engage the derrick structure of the well pumping unit and reciprocate vertically within the derrick structure. A cable sometimes is attached, on one end, to the sliding member or the guides and, on the other end, to the polish rod assembly to translate the orbital movement of the chain into vertical movement on the polish rod assembly.
The member which is attached to the endless chain may also be a rotatable bracket which is fixedly attached to the endless chain on a first end and rotatably attached to the polish rod assembly on a second end. The polish rod assembly must of course be limited to vertical movement. The polish rod assembly is thus oriented along an axis centered with respect to the endless chain and sprocket assembly. As the well pumping unit operates, the first end of the bracket moves in a loop with the endless chain. Since the bracket is rotatably connected to the polish rod assembly, the second end of the bracket reciprocates in a vertical direction. Essentially, the first end of the bracket moves in a loop around the second end, which is reciprocating vertically.
A counterweight is frequently employed in these pumping units to offset the weight of the polish rod assembly. Such counterweights are extremely important in deep wells due to the relatively high weight of the polish rod assembly. The counterweight and the polish rod assembly are usually positioned on opposite sides of a pulley or sprocket. When so positioned, the counterweight offsets the weight of the polish rod assembly to reduce the load which must be raised to operate the polish rod assembly.
It is known to attach the counterweight and the polish rod assembly to the guides or the bracket by cables or chains. In the alternative, the polish rod assembly may be connected to the guides or bracket and the counterweight attached directly to the polish rod assembly (and not directly to the guides or bracket) by a cable or chain.
Examples of the well pumping units described above are disclosed in U.S. Pat. No. 1,599,395 issued to Hards on Sept. 7, 1926, U.S. Pat. No. 1,637,078 issued to Hill on Jul. 26, 1927, U.S. Pat. No. 1,756,089 issued to Hunter on Apr. 29, 1930, U.S. Pat. No. 1,787,164 issued to Parkin on Dec. 30, 1930, U.S. Pat. No. 1,848,530 issued to Hunter on Mar. 8, 1932, U.S. Pat. No. 1,970,620 issued to Park on Aug. 21, 1934, U.S. Pat. 2,292,427 issued to Blackburn on Aug. 11, 1942, U.S. Pat. No. 2,351 183 issued to Blackburn on Jun. 13, l944, U.S. Pat. No. 2,520,187 issued to Wilshusen et al on Aug. 29, 1950, U.S. Pat. No. 2,555,574 issued to Crawford on Jun. 5, 1951, U.S. Pat. No. 2,987,928 issued to Tedford on Jun. 13, 1961, U.S. Pat. No. 3,153,387 issued to Sadouet on Oct. 20, 1964 and U.S. Pat. No. 3,279,266 issued to Dobbs on Oct. 18, 1966.
It is also known in such well pumping units to have a single member function as the guide and the counterweight, and to attach the polish rod assembly to this combination guide/counterweight. Such a well pumping unit is disclosed in U.S. Pat. No. 2,977,808 issued to Dobbs on Apr. 4, 1961.
In addition, well pumping units have been developed wherein the mechanism translating the rotational motion into vertical motion includes a continuous belt or chain driven by a drive mechanism in a loop around rollers or sprockets, and a pitman arm. One end of the pitman arm is attached to the flexible belt or chain. The other end of the pitman arm is attached to a counterweight assembly. One end of a belt and pulley assembly is attached to the counterweight assembly. The other end of the belt and pulley assembly is attached to the polish rod assembly. Such well pumping units are disclosed in U.S. Pat. No. 4,651,582 issued to Bender on Mar. 24, 1987 and my co-pending application, Ser. No. 048,933, filed May 12, 1987, now abandoned;
All these prior well pumping units, while they may be functional, suffer inefficiencies. Moreover, many of the pumping units may not be as durable as desired due to internal and external stresses generated during operation of the well pumping units.
One method of reducing the stress on a well pumping unit is by using a belt system instead of chains or cables. A well pumping unit employing a belt drive system is disclosed in U.S. Pat. No. 4,519,262 issued to Le et al on May 28, 1985. U.S. Pat. No. 4,651,582 employs belts to connect a counterweight assembly, a pulley assembly and a polish rod assembly.
While the well pumping units discussed above have been steps forward in the technology, there is always a need in this art for a more efficient well pumping unit which generates more fluid from the well per unit of power expended to operate the well pumping unit. Any improvement in efficiency results in great savings in the industry. Moreover, there is always a need in the art for a well pumping unit which is designed to minimize the stresses on the unit as the unit operates. This results in a more durable pumping unit, and also decreases the initial capital expenditures to construct the unit.
This invention fulfills these needs, as well as other needs which will become apparent to those skilled in the art once given this disclosure.